Kota -
Honestly, I don't have much experience with Play-Fi. As an integrator by trade, we tend to take a little different approach for whole-house music systems. As for Mac, I've never NOT liked anything digital they've done. Their DACs have always been quiet and smooth sounding. I don't necessarily agree with their stance on MQA but that's another story. I suspect this unit is no different. That said, it is out of production and limited to dealer's stock on hand if you want a new unit. I'm not yet aware of a direct replacement.
I just did a cursory search for Play-Fi "transport" devices you could use with a McIntosh DAC. Finding one new that'll work in a Hi-Fi system seems a little difficult these days so if Play-Fi is important to you, I think I'd call around and try to find an MB20 soon!
Micah